BACKGROUND.
The sensitive detection of circulating tumor cells and micrometastases may have important therapeutic and prognostic implications. METHODS. The molecular detection of occult tumor cells can be accomplished by amplifying tumor specific abnormalities present in the DNA or mRNA of malignant cells with the polymerase chain reaction (PCR). This approach has been used mainly for hemato-lymphoid malignancies. The other main PCR strategy for the detection of minimal residual disease (MRD) involves amplification of tissue-specific mRNA. This method was applied for the detection of occult disease in solid tumors. RESULTS. PCR was shown to be superior to conventional techniques in detecting circulating tumor cells and micrometastases allowing the identification of 1 tumor cell diluted with 10h-lO' normal cells. The central question of whether PCR positivity reliably predicts relapse remains unanswered for many tumor types. Serial analysis of a large number of samples is needed and currently undertaken in many institutions. CONCLUSIONS. PCR is a highly sensitive method for the detection of circulating tumor cells and micrometastases in solid and hematopoietic malignancies. If PCR positivity is found to be a reliable tool, this will likely have a major impact on the treatment of many cancers. Patients could be selected for systemic therapy at an earlier stage when the metastatic tumor burden is low. PCR may improve the preoperative staging of patients with epithelial malignancies and therefore help avoid unnecessary radical procedures. Furthermore, this test may be useful in monitoring the effectiveness of adjuvant therapy, the intensity and duration of which is tailored to the individual patient. The impact of this PCR based approach on clinical oncology is likely to be profound. Cancer 1996; 7810-6.